It is often desirable to effect electrical control of certain devices from a remote location or to sense some physical parameter at one point and to process and display the data at some remote point. For example, speed and distance data are often sensed electronically at the wheel of a vehicle and processed by a remote computer which converts time-dependent pulses from a wheel rotation sensor into instantaneous velocity or a summed measure of distance. Various means have been used to accomplish transmission of such pulse data between the remote points. Direct wiring between the sensor and the computer is commonly used, however such direct wiring is often cumbersome or inconvenient on some vehicles such as bicycles.
Bicycling computers typically employ a magnetically sensitive switch on the bicycle frame and a magnet on a road wheel. The switch/magnet pair is mounted so that the switch is closed by detection of the magnet once for each rotation of the wheel. Electrical wires connect the switch with a computer typically incorporating an oscillator, pulse detector/counter, arithmetic unit, and data storage for determining velocity, distance, or various derivatives thereof. A visual display such as an LCD is often used to present the calculated data to the user. Typical devices are shown in U.S. Pat. No. 3,898,563 to Erisman, U.S. Pat. No. 4,007,419 to Jasmine, U.S. Pat. No. 4,071,892 to Genzling, U.S. Pat. No. 4,156,190 to Chittenden, U.S. Pat. No. 4,352,063 to Jones, and U.S. Pat. Nos. 4,633,216, 4,636,769, and 4,642,606 to Tsuyama. U.S. Pat. No. 4,334,190 to Sochaczevski and U.S. Pat. No. 4,434,801 to Jimenez et al. teach similar monitoring devices. However, such devices have the problem that the wires used to connect the sensors and the computer are often aesthetically intrusive, functionally cumbersome, and subject to being damaged during use.
Some remote sensor devices utilize wireless telemetry to transmit pulse data or other signals to a processor or display unit. For example, U.S. Pat. No. 4,625,733 to Saynajakangas teaches wireless telemetry of pulse data between a user's chest and a remote display unit. However, such remote sensor devices have no particular application to the technical problems encountered in the field of cycling computers. The typical devices tend to have complex transmitter and receiver units and requisite amplifier circuits which make them undesirable for bicycling uses where low unit cost, power consumption, and size are key factors. In addition, the transmitters typically radiate signal energy over a broad three-dimensional field which makes them unsuitable for bicycling use where interference from an adjacent bicycle with a similar transmitter/receiver could produce erroneous speed and distance measurements.
Furthermore, EMI or RFI may be present in the environment where such remote control or telemetry function is desired. Such interference may be generated by electrical appliances such as televisions, computers, and monitors, anti-theft devices, motor vehicle ignition systems, etc., as well as by operation of two telemetry devices in close proximity to each other. Operation of a receiver circuit in the presence of stray RF interference would produce high, inaccurate speed readings which, over a period of time, would produce erroneous average speed, distance, and other readings.
A typical approach to such interference problems might include reprogramming the processor unit to filter or mask out signals which fall outside of acceptable limits. However, reprogramming the processor unit would involve considerable complexity and expense, and would not prevent inaccurate readings within the defined limits. In addition, such filtering or masking would not solve the problem of adjacent operation of similar transmitter/receiver units with similar operating parameters.